The invention relates to a chain of rolling elements comprising a plurality of rolling elements and an elongate carrier belt, wherein the carrier belt comprises a plurality of recesses for receiving the rolling elements, a plurality of retainers for retaining the rolling elements received in the recesses and at least one elongate flexible element for connecting the retainers and wherein two lateral edge portions and a central portion connecting them can also be distinguished on the carrier belt, the retainers being connected to the at least one flexible element in the lateral edge region of the carrier belt.
2. Background of the Invention
A chain of rolling elements of this type is known, for example, from Japanese patent laid-open print 5-52217 (1993) to Japanese patent application 3-235563 (1991). The known chain of rolling elements comprises a plurality of balls arranged in recesses in a carrier belt. Between each two successive balls there is arranged a retainer which comprises, on its sides leading or trailing in the longitudinal direction of the carrier belt, a respective retaining face for sliding engagement with the leading or trailing ball. The retainers are connected to one another by two flexible strip elements and form the carrier belt together with it.
The known ball chain has the advantage that the balls can be arranged in close succession, i.e. with minimal spacing from one another. The ratio of the ball diameter to the spacing between the centres of two adjacent balls is approximately 1:1. Owing to the resultant high ball density, the known ball chain has a high load-carrying or load-bearing capacity. However, the stiffening of the carrier belt accompanying the fastening of the two strip elements to the retainers in the region between two successive balls is disadvantageous. The strip elements of the carrier belt are able to react to bending of the carrier belt round an axis extending parallel to the transverse direction of the carrier belt, for example in the deflection portions of the race of a linear bearing, only in the region of their lateral contact with the balls but not in the region of their lateral fastening to the retainers.
The resultant relatively pronounced bending of the carrier belt in the region of its lateral contact with the balls leads to a corresponding restoring force of the carrier belt, resulting from the elasticity of the carrier belt material, into its rectilinear position. This restoring force influences the movement of the balls in the deflection portions of the race owing to the retaining of the balls by the carrier belt. In a linear bearing equipped with the known chain of rolling elements, the pronounced bending of the carrier belt can lead to more pronounced generation of noise and to increased friction between the strip elements and the guide grooves.
Further chains of balls with balls in close succession are disclosed, for example, in U.S. Pat. Nos. 2,897,021 and 3,292,981. In these ball chains also a retainer is arranged in each case between two successive balls, the retainer comprising a retaining face for sliding engagement with the leading ball as well as a retaining face for sliding engagement with the trailing ball.
A further non-generic chain of rolling elements is known from Japanese patent laid-open print 62-242126 (1987) to Japanese patent application 60-253865 (1985). In the chains of rolling elements known from FIGS. 5 and 6 thereof, each rolling element is retained by two retainers associated with it and only with it. Therefore, between two successive rolling elements there are provided two physically separated retainers which are arranged in a central portion of the carrier belt with predetermined spacing from one another.
The carrier belt of the known chain of rolling elements has the advantage that it can be bent round an axis extending parallel to the transverse direction not only in the regions of its lateral contact with the rolling elements but also in the regions between two successive rolling elements. As the number of bending points is twice that in JP-A-5-52217 (1993), the carrier belt is bent less at each individual bending point with equal curvature of a deflection portion of the race and influences the running of the rolling elements to a correspondingly smaller extent and this results in smoother running of a linear bearing equipped with the known chain of rolling elements. The chain of rolling elements known from JP-A-62-242126 (1987) has the drawback, however, that the rolling elements are arranged in a loose succession, i.e. with relatively great mutual spacing, to provide the space required for the separate retainers. The ratio of the ball diameter to the spacing of the centres of two adjacent balls is approximately 1:1.5. The resultant lower density of rolling elements is accompanied by a corresponding reduction in the load-carrying capacity of the chain of rolling elements.
DE-PS 835 718 discloses a chain of rolling elements in which the spacing between successive rolling elements is about twice the diameter of the rolling elements. The rolling elements are retained by tongues arranged therebetween of a spring steel strip carrying them. A chain of rolling elements with rolling element spacing of similar size, i.e. similarly loose succession of rolling elements, is disclosed in U.S. Pat. No. 2,557,476.
DE 36 35 261 A1 describes a ball chain with average ball spacing. In other words, the ratio of the ball diameter to the spacing of the centres of successive balls is about 1:1.25. Each of the balls is associated with mutually separated retainers arranged between the balls. Therefore, the retainers are very small and can barely retain the balls.
The ball chain known from DE 29 06 128 A1 is formed from a plurality of chain units which are formed independently of one another and each serve to guide only one of the balls. This arrangement therefore results in a loose succession of balls. The orifices receiving the balls do not retain the balls. Therefore, the chain units also comprise guide blocks which are separate from the receiving orifices and centre the chain units in the ball channel and, in particular its deflection portions with respect to the running of the balls.
Reference is also made to DE 37 09 039 C2, DE 89 14 085 U and U.S. Pat. No. 2,566,421.
Accordingly, it is an object of the present invention to provide a chain of rolling elements which is distinguished by a high load-carrying or load-bearing capacity and also by smooth running.
According to a first aspect of the invention, this object is achieved by a chain of rolling elements comprising a plurality of rolling elements arranged in close succession and an elongate carrier belt with a plurality of recesses for receiving the rolling elements, a plurality of retainers for retaining the rolling elements received in the recesses, and at least one elongate flexible element for connecting the retainers, wherein the carrier belt can be split into two lateral edge portions and a central portion connecting them, wherein, moreover, the retainers are connected to the at least one flexible element in the lateral edge regions of the carrier belt, wherein, moreover, separate retainers are associated with successive rolling elements, and wherein at least one retainer associated with each rolling element is provided before and after each rolling element on the at least one flexible element in the longitudinal direction thereof. The term close succession of rolling elements is interpreted according to the foregoing discussion of the state of the art as a succession in which the ratio of the diameter of the rolling elements to the spacing of the centres of successive rolling elements is less than 1:1.5, preferably less than 1:1.25, most preferably approximately 1:1.
This solution principle is based on the combined effect of two groups of features. On the one hand, the carrier belt is flexibilized in the region between successive rolling elements since separate retainers are associated with each rolling element, and this has an advantageous effect on the smoothness of running. Since the retainers are also connected to the flexible element in the lateral edge regions of the carrier belt, the necessary freedom for bringing together the rolling elements is simultaneously achieved in the region of the central portion of the carrier belt. The resultant increase in the number of rolling elements per length unit, i.e. the resultant increase in the density of rolling elements, has a desirable effect on the load-carrying or load-bearing capacity of the chain of rolling elements.
It should be noted that the chain of rolling elements according to the invention, in particular its carrier belt, is simple to produce. Thus, the carrier belt can be produced in one piece, for example from a plastics material from the group comprising elastomers such as, for example, polyurethane, Hytrel or the like, preferably as an injection moulding.
According to a first variation, in the longitudinal direction of the at least one flexible element before and after at least one rolling element there are provided in each case at least two retainers associated with this rolling element. These retainers can be arranged on both sides of the central portion of the carrier belt in its lateral portions so that each rolling element, for example each ball, is received in a cage formed by at least four retainers.
If two retainers, of which one is provided above a main plane of the carrier belt and one is provided below this main plane, are arranged directly above and below one another, these two retainers provide a common retaining face extending over a large angular range which ensures that the rolling element is retained securely.
The rolling element can be retained particularly securely if it is retained on the one hand by the peripheral face of the recess receiving this rolling element and on the other hand by a plurality of, preferably at least four, combinations of retainers, which are distributed, preferably uniformly, around the periphery of this recess and of which the retaining faces extend in each case above and below the main plane of the carrier belt, i.e. above and below the peripheral face of the recess.
According to a second variation, at least one of the retainers can be designed as a full ring or half ring which extends in the form of an arc from one edge portion to the other respective edge portion above and/or below a main plane of the carrier belt. With this variation, the retainers in the region of the longitudinal centre of the main plane of the carrier belt again do not rest on the rolling elements so the rolling elements can be brought very close to one another. Owing to the arcuate design of the retainer, furthermore, extensive contact between the retainer and the rolling element and therefore secure retaining of the rolling element are achieved.
An arrangement which is particularly flexible with respect to bending round an axis extending substantially parallel to the transverse direction of the carrier belt can be achieved if a half ring associated with a first rolling element and a second half ring adjacent to this first half ring and associated with the subsequent rolling element are arranged on different sides of the main plane of the carrier belt. With this design, there is in fact no risk that these two retainers will come into contact during bending of the carrier belt and thus limit the attainable bending angle.
To ensure that the rolling elements are retained securely in the aforementioned variations, even when the chain of rolling elements is stressed, for example in the deflection portions of the channel, it is proposed that the at least one flexible element is designed in the form of a ladder with two longitudinally extending spar elements and a plurality of rung elements connecting these spar elements and extending substantially in the transverse direction of the carrier belt. In the first variation, these rung elements alone produce the connection between the two spar elements and the retainers arranged thereon. In the second variation, the arcs projecting from the main plane of the guide belt are strengthened in the transverse direction of the carrier belt by these rung elements. For example, a load-induced deformation of a circular retainer to an ellipse is at least complicated if not completely prevented by a rung element of this type. Furthermore, the rung elements which can be relatively thin in design in the central portion of the carrier belt in the main plane thereof can form an additional securing means which prevents direct contact between successive rolling elements even when the chain of rolling elements is loaded and therefore averts excessive wear of these rolling elements.
According to a further variation, at least one of the retainers is designed as a full disc or half disc which extends between the edge portions above and/or below a main plane of the carrier belt. With this variation, it is preferred with respect to maximum flexibility of the carrier belt in the region between two successive rolling elements if the at least one flexible element comprises only two flexible strip elements which are associated with the two edge portions of the carrier belt but not bars transversely connecting these strip elements. Contact between two successive rolling elements in the region of the central portion of the main plane of the carrier belt is prevented therein by the two actual disc-shaped retainers which have a small wall thickness of at most about 0.2 times rolling element diameter, preferably at most about 0.1 times rolling element diameter in the region of the central portion of the main plane of the carrier belt in the longitudinal direction thereof to allow a close succession of rolling elements.
In all the above-discussed variations, it is possible, despite the close succession of rolling elements, for two adjacent retainers associated with successive rolling elements to have predetermined spacing from one another in the main plane of the carrier belt. As a result, only the material of the strip or spar elements and optionally of the rung elements needs to be deformed during bending of the carrier belt round an axis extending parallel to the transverse axis in the region between two successive rolling elements while the retainers are subjected to substantially no deformation even in the region of their connection to the strip or spar and rung elements.
With small spacing, which even disappears in extreme cases, between the retainers in the main plane of the carrier belt, high flexibility of the carrier belt in the region between successive rolling elements can be ensured if the spacing between two adjacent retainers associated with successive rolling elements increases as the distance from the main plane of the carrier belt increases. This avoids the risk of contact between adjacent retainers which restricts the bending angle, even in the case of small bending angles. It is particularly preferred if the spacing between the two retainers, at least in a portion adjacent to the main plane of the carrier belt, increases monotonically as the distance from the main plane of the carrier belt increases.
According to a further aspect, the above-described object of the invention is achieved by a chain of rolling elements comprising a plurality of rolling elements arranged in close succession and an elongate guide belt with a plurality of recesses for receiving the rolling elements, a plurality of spacers and at least one elongate flexible element for connecting the spacers, wherein the guide belt can be split into two lateral edge portions and a central portion connecting them, wherein moreover the spacers have a contact face for a leading rolling element at a leading end and a contact face for a trailing rolling element at a trailing end, and wherein the contact faces associated with a rolling element are part of a cylindrical face of which the diameter is greater than the diameter of the rolling elements. The term close succession of rolling elements is again interpreted as a succession in which the ratio of the diameter of the rolling elements to the spacing between centres of successive rolling elements is less than 1:1.5, preferably less than 1:1.25, most preferably approximately 1:1.
In this chain of rolling elements, the rolling elements are not retained but merely guided in the recesses of the guide belt so the guide belt, in particular in the region of the deflection parts of the race, cannot exert on the rolling elements a bend-induced force which influences the movement thereof, and this is accompanied by corresponding low noise generation. The close succession of rolling elements is ensured, as in the chain of rolling elements known from JP-A-5-52217, in that, between two successive rolling elements, there is arranged only a single element which, in contrast to JP-A-5-52217, however, does not have a retaining function but merely a guiding and spacing function.
For introducing the above-described chain of rolling elements, the guide belt received in an assembly tube and already equipped with rolling elements can be brought toward the channel of the linear guide unit and can be transferred directly from the assembly tube into the channel. Simple assembly of the chain of rolling elements according to the invention is therefore ensured according to the further aspect of the invention even though the rolling elements are not retained in the guide belt.
In a development of this chain of rolling elements which merely guides the rolling elements it is proposed that the cylindrical face extends over a greater height in the central portion of the guide belt than in the two lateral portions, the cylindrical face additionally or alternatively extending in the central portion of the guide belt over a height which is smaller than the diameter of the rolling element guided by this cylindrical face, but preferably greater than the radius thereof.
According to a further aspect, the invention relates to a chain of rolling elements comprising a plurality of rolling elements arranged in close succession and an elongate carrier belt with a plurality of recesses for receiving the rolling elements, a plurality of retainers or spacers for the rolling elements received in the recesses and at least one elongate flexible element for connecting the retainers or spacers, wherein the two longitudinal ends of the carrier belt are prepared for connection to a further longitudinal end or are connected to a further longitudinal end. With this design of the chain of rolling elements, for which independent protection is sought, hooking or blocking of the respective leading end of the guide belt in the rolling element channel and, in particular, the deflecting portions thereof can at least be complicated, if not completely avoided. Smoother running of a guide device equipped with at least one such chain of rolling elements, for example a linear guide, can therefore be achieved.
The further longitudinal end can be the other respective longitudinal end of the same carrier belt. Alternatively, however, the further longitudinal end can be a longitudinal end of a further carrier belt. The last-mentioned alternative allows long chains of rolling elements to be assembled in modular fashion from a plurality of shorter chains of rolling elements of identical or different length and/or design.
According to a variation, the ends of the chain of rolling elements or the chains of rolling elements can be mutually connected in an interlocking manner. For example, coupling elements which can be mutually connected at the two longitudinal ends and can preferably be detachably mutually connected can be provided for this purpose. The coupling elements can comprise, for example, a coupling recess and a coupling peg designed to engage in the coupling recess.
The two longitudinal ends of the carrier belt can additionally or alternatively also be mutually connected in a non-positive manner, for example by welding, adhesion or the like.
According to a further aspect the invention relates to an arrangement of chains of rolling elements comprising a plurality of chains of rolling elements. The individual chains do not necessarily have to have the same construction. On the contrary it is possible to use chains of rolling elements having retainers and chains of rolling elements having spacers. Additionally, the individual chains in the rolling element revolutions can succeed one another in a loose arrangement, i.e. without being linked, or in a connected arrangement. Of course, mixed forms are also possible, i.e. in which some of the individual chains are connected with each other, whereas they are not connected with other individual chains or/and groups of individual chains. Such an arrangement of chains of rolling elements has the advantage that it can easily be manufactured and stored, as for each application an arrangement of chains of rolling elements having a suitable length and shape can be modularly put together from a plurality of prefabricated shorter chains of rolling elements having the same or a different length and/or shape.
To avoid any misunderstanding it should be pointed out that when, in connection with the present invention, a xe2x80x9cpluralityxe2x80x9d of rolling elements and/or chains of rolling elements is mentioned, a plurality always refers to at least two such rolling elements and/or chains of rolling elements.
According to a further aspect, the invention relates to a chain of rolling elements, which comprises a plurality of rolling elements arranged in close succession as well as an elongate guide belt with a plurality of spacers and at least one elongate flexible connecting element, which is connected with lateral edge portions of the spacers, in such an arrangement that, between the spacers projecting in a transverse direction from the connecting element, a plurality of recesses are formed for the loose reception of the rolling elements. Such chains of rolling elements are used, for example, in linear guides, such as ball or roll guides, and in linear drives such as ball thread drives.
Above two solution principles are discussed, which both serve for increasing the load-bearing capacity and smooth running of chains of rolling elements. In both cases, high load-bearing capacity is achieved by a close succession of the rolling elements. On the one hand, it is proposed that when the guide belt comprises retaining elements, which prevent the rolling elements from falling out of the guide belt, special retaining elements are assigned to each of the rolling elements. As a result of this measure, the number of points facilitating bending of the guide belt is doubled. The resulting flexibilization of the guide belt has the effect of ensuring that the guide belt cannot influence the operation of the rolling elements in a noise-producing manner. On the other hand, it is proposed that the rolling elements should no longer be retained in the recesses of the guide belt but loosely taken up, i.e. at most be guided. The resulting possibility of relative movements of the guide belt and rolling elements in the running channel, i.e. the resulting decoupling of guide belt and rolling elements, at least in a height direction extending orthogonally both in the longitudinal and transverse directions, has a beneficial effect on the development of noise. A drawback of the last-named embodiment, however, might be a relatively high wear.
For this reason, it is another object of the invention to further improve a chain of rolling elements with rolling elements loosely taken up in the recesses of the driving belt in respect of a higher working life or a higher total period of operation.
This object is achieved, in accordance with a first sub-aspect, by a generic chain of rolling elements, in which the dimension of the spacers taken in the longitudinal direction of the guide belt is smaller in their lateral edge portions than the radius of the rolling elements.
In accordance with a second sub-aspect, this object is achieved by a generic chain of rolling elements, in which the connecting element between connecting sections with consecutive spacers comprises, in each instance, a free longitudinal section, the length of the free longitudinal sections being greater than the length of the connecting sections.
As a result of each of these two measures, flexibilization of the guide belt is achieved, however not by increasing the number of bending points but by reducing the length of the spacers stiffening the connecting elements. That this measure leads to an increase in working life, could not be expected at the outset. A reduction in possible contact surfaces between rolling elements and guide belt as a result of friction inevitably causes higher wear on the remaining contact surfaces. Surprisingly, however, it has been shown that this effect on the lateral contact surfaces, subject to special load, of the rolling elements on the connecting elements is overcompensated by their greater flexibility and the associated reduction in bending stress.
It should be noted that as above, by a close succession of rolling elements a succession is understood, in which the ratio of the rolling element diameter to the distance between the center points of consecutive rolling elements is less than 1:1.5, preferably less than 1:1.25 and most preferably approximately 1:1.
Even greater flexibilization of the guide belt can be achieved by making the longitudinal dimension of the spacers in their lateral edge portions less than 50%, preferably less than 20%, of the radius of the rolling elements or by making the length of the free longitudinal sections double, preferably ten times, the length of the connecting elements.
An essentially unchanged size and shape of the recesses taking up the rolling elements can be secured by giving the guide belt an essentially ladder-like structure i.e. for example, by having the guide belt comprise at least two elongate flexible connecting elements spaced apart in the transverse direction, which receive the spacers between them.
As a further development of the invention, it is proposed that the surfaces of the spacers limiting the recesses extend essentially orthogonally to the longitudinal direction of the guide belt. This facilitates a particularly flexible construction of the guide belt since, as a consequence, the length of the connecting sections stiffening the guide belt corresponds only to the thickness of the spacers in their central portion separating the rolling elements. The value of this thickness is limited downwards only by the desired stability of the guide belt, which is preferably manufactured as a one-piece plastic part, advantageously in the injection molding process. Furthermore, this embodiment has the advantage that one and the same guide belt can be combined with different types of rolling elements, for example balls and rolls.
If the surfaces limiting the recesses of consecutive spacers exhibit, in the vicinity of the lateral edge portions of the spacers, a smaller distance between them than in the area of a central portion arranged between the edge portions, this is advantageous, both when balls are used as rolling elements and when rolls are used as rolling elements. When rolls are used, these all come into play with the spacers in the surface sections of lower longitudinal spacing so that it is also only in these surface sections of lower longitudinal spacing that there is any danger of the stripping of lubricant from the rolling element surface. In the surface sections of greater longitudinal spacing, on the other hand, the surface of the rolling elements also remains securely wetted with lubricant when passing the spacers so that the lubrication of the running channel in which the chain of rolling elements moves, is guaranteed.
When balls are used, the problem of lubricant stripping occurs only to a non-critical extent as a consequence of the smaller contact surface with the spacers. In this case, the advantage of surface sections of greater longitudinal spacing lies in the fact that the closeness of the succession of balls and thus the load-bearing capacity of the chain of rolling elements can be increased. Since the surface sections of greater longitudinal spacing only have to bridge the central portion of the spacers, the spacers can be made correspondingly thinner in their central portion than would be possible with a spacer, which extends over the entire distance between both elongate flexible connecting elements with constant thickness.
In the case of the use of balls as rolling elements, furthermore, it is conceivable that the surface sections of greater longitudinal spacing can be formed at least partially as part of a cylinder surface, the cylinder axle thereof extending advantageously in a direction proceeding orthogonally to both the longitudinal direction and transverse direction of the guide belt.
In order to be able to prevent any stripping of lubricant from the running surfaces of the running channel, in which the chain of rolling elements moves, it is proposed that at least one part of the spacers exhibits a height, which is smaller than the diameter of the rolling elements. Additionally or alternatively, however, it is also possible for at least some of the spacers to exhibit on boundary edges, which limit the spacer in a height direction orthogonal to both the longitudinal direction and the transverse direction of the guide belt, recesses, which facilitate the passage of lubricant when the chain of rolling elements moves in the longitudinal direction of the guide belt.
According to a further aspect, the invention relates to a arrangement of chains of rolling elements, comprising at least one chain of rolling elements with a plurality of rolling elements and an elongate supporting and/or guiding belt, which exhibits a plurality of recesses for the take-up of the rolling elements, a plurality of retainers and/or spacers for the rolling elements received in the recesses and at least one elongate flexible element for connecting of the retainers and/or spacers, whereby, between a trailing longitudinal end of a supporting and/or guiding belt and a trailing end of a supporting and/or guiding belt, a separating rolling element is arranged keeping these two longitudinal ends at a distance. The two longitudinal ends may belong to one and the same chain of rolling elements as well as to two different chains of rolling elements.
From the state of the art, on the one hand, arrangements of chains of rolling elements are known in which the leading longitudinal end and the trailing longitudinal end are fixed together, for example by a locating mechanism or such like. On the other hand, arrangements of chains of rolling elements known, in which the two longitudinal ends lie adjacent to one another with relatively free movement between them. The first-named embodiment has the disadvantage that corresponding room must be provided for the linking of the two longitudinal ends, which impairs the load-bearing capacity of the known arrangement of chains of rolling elements, at least in the area of the connection of the two longitudinal ends. The second-named embodiment has the disadvantage that the space between the longitudinal ends permits uncontrolled elongation of the chain of rolling elements, which may lead to fracture.
In contrast, the solution according to the invention specified above prevents such uncontrolled elongation in an amazingly simple manner. Furthermore, the solution of the invention makes it possible for the rolling elements to be arranged consecutively also in the area of the transition from a leading to a trailing chain end, with the same closeness with which they are also arranged over the remaining entire length of the chains of rolling elements. Thus the arrangement of chains of rolling elements exhibits high load-bearing capacity in the connection area as well.
At this point attention is drawn to the fact that the idea of providing a separating rolling element between consecutive longitudinal ends of chains of rolling elements, is not restricted to chains of rolling elements, in which the rolling elements are taken up loosely in the recesses of the guide belt, but may also be implemented in those chains of rolling elements, in which the rolling elements are held in these recesses.
If an end surface of at least one of the longitudinal ends, preferably at least the trailing longitudinal end, is formed at least partially in accordance with the external peripheral surface of the separating rolling element, the separating rolling element may be brought into guiding and/or centering engagement with this longitudinal end. The consequence is that the deflection of the guide belt in a curved section of the running channel does not at least not exclusively result from the interaction of the guide belt with the boundary walls of the running channel. Rather this longitudinal end is carried along and/or deflected by the associated separating rolling element, which has a beneficial effect on the smooth and quiet running of the rolling element chain arrangement according to the invention and/or of the chain of rolling elements according to the invention.